Advances in combined orthodontic and surgical treatment have made it possible to correct or significantly improve dentofacial deformities which could not be treated previously, with significant progress continuing to occur at a rapid rate. Although the long-term results of orthognathic surgery are stable in most instances, there are some post-treatment changes in morphology in almost all patients and significant relapse in a few. The alterations in jaw position and oral cavity volume produced by this surgery require considerable physiologic adaptation, and it is likely that the extent of post-treatment morphologic change is related to the extent and pattern of physiologic adaptation. In this project, patients undergoing surgical-orthodontic treatment through the UNC Dentofacial Program will be studied. Morphologic stability will be evaluated and correlations will be sought between post-treatment morphologic changes and (1) posture of the head, mandible and tongue as evaluated from natural head position cephalometric radiographs, (2) lip pressures and function, measured with miniature intra-oral pressure transducers, (3) the balance of tongue and lip forces across the lower dental arch, (4) respiratory mode, as evaluated using the newly-developed SNORT apparatus for measurement of nasal/oral airflow ratios, (5) vertically directed tongue pressures, and (6) occlusal forces during swallowing, chewing and maximum effort, as evaluated using piezo-electric force transducers. The data base will be used to test a series of specific hypotheses related to clinically important questions. The project should provide insight into soft tissue function as a factor in the etiology of dentofacial deformity as well as a determinant of post-treatment stability.